Intervertebral spacer device utilizing a spirally slotted belleville washer having radially spaced concentric grooves

Abstract

An intervertebral spacer device having a pair of opposing plates for seating against opposing vertebral bone surfaces, separated by at least one spring mechanism. The preferred spring mechanism is at least one spirally slotted belleville washer having radially spaced concentric grooves. In a preferred embodiment there is a single such belleville washer which is modified to mount onto a ball-shaped head. The lower plate of this embodiment includes a post extending upwardly from the inner surface of the plate, the post including a ball-shaped head. The modified belleville washer can be rotatably mounted to the head such that the wider portion of the washer seats against the upper plate.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application is a continuation application of U.S. patent application Ser. No. 09 / 975,471 (filed Oct. 11, 2001) entitled “Intervertebral Spacer Device Utilizing A Spirally Slotted Belleville Washer Having Radially Spaced Concentric Grooves”, now U.S. Pat. No. 6,863,688 (“the '688 patent”), which is a continuation-in-part of U.S. patent application Ser. No. 09 / 970,479 (filed Oct. 1, 2001) entitled “Intervertebral Spacer Device Utilizing A Spirally Slotted Belleville Washer Having Radially Extending Grooves”, now U.S. Pat. No. 6,669,730 (“the '730 patent), which is a continuation-in-part of Ser. No. 09 / 968,046 (filed Oct. 1, 2001) entitled “Intervertebral Spacer Device Utilizing A Belleville Washer Having Radially Extending Grooves”, now abandoned. of the above mentioned applications are hereby incorporated byFIELD OF THE INVENTION[0002]This invention relates generally to a spinal implant assembly for implantation into the intervertebral...

AI Technical Summary

Benefits of technology

[0019]In the preferred embodiment of the present invention, a single modified belleville washer, which is of the slotted variety and has radially spaced concentric grooves as described above, is utilized in conjunction with a ball-shaped post on which it is free to rotate through a range of angles (thus permitting the plates to rotate relative to one another through a corresponding range of angles). More particularly, this embodiment comprises a pair of spaced apart base plates, one of which is simply a disc shaped member (preferably shaped to match the end of an intervertebral disc) having an external face (having the porous coating discussed above) and an internal face having an annular retaining wall (the purpose of which will be discussed below). The other of the plates is similarly shaped, having an exterior face with a porous coating, but further includes on its internal face a central post portion which rises out of the internal face at a nearly perpendicular angle. The top of this post portion includes a ball-shaped knob. The knob includes a central threaded axial bore which receives a small set screw. Prior to the insertion of the set screw, the ball-shaped head of the post can deflect radially inward (so that the ball-shaped knob contracts). The insertion of the set screw eliminates the capacity for this deflection.

[0020]As introduced above, a modified and spirally slotted belleville washer having radially spaced concentric grooves is mounted to this ball-shaped knob in such a way that it may rotate freely through a range of angles equivalent to the fraction of normal human spine rotation (to mimic normal disc rotation). The belleville washer of this design is modified by including an enlarged inner circumferential portion (at the center of the washer) which accommodates the ball-shaped portion of the post. More particularly, the enlarged portion of the modified belleville washer includes a curvate volume having a substantially constant radius of curvature which is also substantially equivalent to the radius of the ball-shaped head of the post. The deflectability of the ball-shaped head of the post, prior to the insertion of the set screw, permits the head to be inserted into the interior volume at the center of the belleville washer. Subsequent introduction of the set screw into the axial bore of the post prevents the ball-shaped head from deflecting. Thereby, the washer can be secured to the ball-shaped head so that it can rotate thereon through a range of proper lordotic angles (in some embodiments, a tightening of the set screw locks the washer on the ball-shaped head at one of the lordotic angles).

[0021]This assembly provides ample spring-like performance with respect to axial compressive loads, as well as long cycle life to mimic the axial biomechanical performance of the normal human intervertebral disc. The spiral slots and radially spaced concentric grooves of the belleville washer allow the washer to expand radially as the slots and grooves widen under the load, only to spring back into its undeflected shape upon the unloading of the spring. As the washer compresses and decompresses, the annual retaining wall maintains the wide end of the washer within a prescribed boundary on the internal face of the base plate which it contacts, and an annular retaining ring maintains the wide end of the washer against the internal face.

Problems solved by technology

It is, however, important to note that the fusion of the adjacent bones is an incomplete solution to the underlying pathology as it does not cure the ailment, but rather simply masks the pathology under a stabilizing bridge of bone.

This bone fusion limits the overall flexibility of the spinal column and artificially constrains the normal motion of the patient.

This constraint can cause collateral injury to the patient's spine as additional stresses of motion, normally borne by the now-fused joint, are transferred onto the nearby facet joints and intervertebral discs.

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